The invention relates to a bunged vessel of thermoplastic material having at least one separately prefabricated carrying and transport ring snapped onto the vessel wall near the associated head of the vessel, with an outward projection molded onto the upper edge of the ring for the prongs of a handling means.
Plastic vessels thus equipped can be picked up, lifted and transported without manual maneuvers using the conventional fittings of a fork lift truck. Ordinarily, such carrying and transport rings have a cross-section with a horizontal and vertical web. The free end of the vertical web is directed towards the respective head of the vessel, and the horizontal web is molded radially outward.
The handling means of lifting and transporting such vessels engages its prongs firstly under the horizontally outward directed web of the ring and behind the vertically upward directed web. The entire load of the vessel is transmitted by the horizontally outward directed web to the lower prong of the handling means, while the prong engaged behind the vertical web secures the vessel against slipping off.
It is known that the carrying and transport ring may be made in one piece with the wall of the vessel. In so doing, the tube extruded into the opened mold is pinched off and welded by the meeting lateral halves of the main mold. The carrying and transport ring regions of the halves of the main mold each contain a vertically displaceable slide with the ring profiles cut into its inner contours. In the blowing operation, the enlarging tube is forced into the recesses between main mold and slide.
Then the slides are closed and the tube material is formed in the ring mold. Wall layers are thus formed, which are welded together by their own heat. In transport or if a filled vessel is dropped, these welds are exposed to high tensile and bending stresses.
From the foregoing it follows that to produce a vessel of this construction, a considerable mold-making outlay must be expended. To avoid this, there have been attempts to weld separately prefabricated carrying and transport rings onto the wall of the vessel, or to snap them into recesses provided for that purpose in the wall of the vessel as blown. In the latter case, the construction of the mold is much simplified because the slides capable of vertical displacement in the halves of the main mold can be dispensed with.
A disadvantage of bunged vessels with carrying transport rings snapped onto the wall of the vessel is the fact that the extension molded onto the top edge of the ring for the prongs of a handling means generally projects beyond the head surface of the wall of the vessel so that the handling means can be applied. The wall of the vessel is in fact cylindrical in shape, and meets the plane of the head of the vessel nearly at right angles. The projection of the ring is disadvantageous because the entire stack load, if several vessels are stacked one upon another, must be assumed by the carrying and transport ring. The ring is moreover unprotected, so that the full impact energy of a dropped vessel will act on the free extremity of the ring. Furthermore, the protruding length of the carrying and transport ring acts as a lever arm, so that if a dropped vessel lands obliquely, the carrying ring may be pried out of its attachment.
It is therefore an object of the present invention to provide a blown plastic bung vessel with a separate, snap-on carry and transport ring such that the complexity of the vessel mold may be greatly reduced.
It is a further object of the invention to provide the carry and transport ring with a means of attachment and location such that it will not be subject to excessive stresses when the vessel is stacked or dropped, while at the same time providing adequate clearance for the prongs of a mechanical handling means.